This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Certain abbreviations that may be found in the description and/or in the Figures are herewith defined as follows:                3GPP third generation partnership project        ACK acknowledge        CDM code division multiplexing        DL downlink (eNB towards UE)        DRX discontinuous transmission        eNB EUTRAN Node B (evolved Node B)        EUTRAN evolved UTRAN (LTE)        FFT fast Fourier transform        DFT discrete Fourier Transformation        DFT-S OFDMA DFT spread OFDMA        HARQ hybrid automatic repeat request        IFFT inverse fast Fourier transformation        LTE long term evolution        MAC medium access control        MM/MME mobility management/mobility management entity        NACK not acknowledge/negative acknowledge        Node B base station        OFDMA orthogonal frequency division multiple access        PDCCH physical downlink control channel        PUCCH physical uplink control channel        RF radio frequency        RS reference symbol        SC-FDMA single carrier, frequency division multiple access        SF spreading factor        UE user equipment        UL uplink (UE towards eNB)        UTRAN universal terrestrial radio access network        
In the communication system known as evolved UTRAN (EUTRAN, also referred to as LTE, E-UTRA or 3.9G), the downlink access technique is OFDMA, and the uplink access technique is SC-FDMA in completed LTE Release 8. A further release of 3GPP LTE, referred to herein as LTE-Advanced (LTE-A) is directed toward extending and optimizing the 3GPP LTE Release 8 radio access technologies to provide higher data rates at low cost. LTE-A is expected to be incorporated into LTE Release 10 which is currently under development, and will continue the Release 8 access techniques noted above.
FIG. 1 reproduces FIG. 4.1 of 3GPP TS 36.300, V8.6.0 (2008-09), and shows the overall architecture of the E-UTRAN system. The EUTRAN system includes eNBs, providing the EUTRA user plane and control plane protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to a Mobility Management Entity (MME) and to a Serving Gateway (S-GW). The S1 interface supports a many to many relationship between MMEs/S-GWs and eNBs.
It has been agreed in LTE-A during RAN1 #61 bis that block spread DFT-S-OFDMA is used as a signaling scheme for HARQ-ACK/NACK on the PUCCH for Release 10 UEs that support more than 4 downlink ACK/NACK bits with carrier aggregation. See for example documents R1-062841 entitled Multiplexing of L1/L2 Control Signalling when UE has no data to transmit (by Nokia); R1-091353 entitled On CSI feedback signalling in LTE-Advanced uplink (by Nokia Siemens Networks and Nokia); and R1-074812 entitled On PUCCH Structure for CQI Report (by NTT DoCoMo, Nokia Siemens Networks, Nokia, Mitsubishi Electric, and Toshiba Corporation). In general the goal of randomization is to limit interfering block spread DFT-signal(s) that originate from adjacent cells such as the two adjacent eNBs shown at FIG. 1.
FIG. 2 illustrates a block level description of block-spread DFT-S-OFDM with SF=5. Data signals from different UEs within a single cell are separated by different block level spreading codes, represented as w. At FIG. 2, a FFT is performed on modulation symbols [d(0), d(1), . . . d(N)] which are then multiplied by the SF=5 elements w0, w1, . . . w4 of one particular UE's spreading code w, parallel IFFTs are done on those five results and the time domain OFDMA symbol is inserted into a transmission frame with reference symbols RSs which the UE sends on the UL.
One challenge in LTE-A at least is that there are not enough block spreading codes available to provide sufficient randomization in the block code domain between cells. But randomization is important for CDM-based schemes such as DFT-S-OFDMA in order to attenuate co-channel interference between the UEs using the same block spreading code. Otherwise transmissions from one UE operating for example at an edge of a first cell might regularly interfere with transmissions from another UE operating in an adjacent cell and using the same block spreading code.
One possible solution is to scramble the encoded bits with DFT-S-OFDMA symbol specific and cell specific scrambling sequences. This is detailed at documents R1-100909 entitled A/N transmission in the uplink for carrier aggregation; and R1-101730 entitled PUCCH design for carrier aggregation, both of which are by Ericsson and ST-Ericsson. But the scrambling sequences need to be DTF-S-OFDMA symbol specific, i.e., vary between DFT-S-OFDM symbols because the same data symbols [d(0), . . . d(N−1)] remain unchanged between the DFT-S-OFDM symbols. It is advantageous to scramble in the time domain (before the FFT or after the IFFT) as shown at FIG. 1 of document R1-101730 to avoid increasing the peak-to-average power ratio (PAR or PAPR). But scrambling before the FFT processing means that instead of one FFT block as in FIG. 2 there would be the added complexity of a separate FFT block immediately upstream of each IFFT block as is shown in FIG. 1 of document R1-101730.
Exemplary embodiments of this invention mitigate co-channel interference by randomizing block-spread transmissions from UEs in adjacent cells without adding the complexity as is noted above, even if there are not enough different block spreading codes to do so directly by assigning a spreading code that is unique to all UEs across all adjacent cells.